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Systems and methods for wireless power transfer

This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 60/841,759, filed on Sep. 1, 2006; U.S. Provisional Application No. 60/894,581, filed on Mar. 13, 2007; and U.S. Provisional Application No. 60/950,192, filed on Jul. 17, 2007, the entire disclosures of which are hereby incorporated by reference.

This application is related to copending application titled THREE-DIMENSIONAL ELECTROMAGNETIC FLUX FIELD GENERATION, Ser. No. ______ [Attorney Docket No. RAIF.004A], filed on the same date as the present application, the entirety of which is hereby incorporated by reference.

1. Field of the Invention

The invention generally relates to electronics, and in particular, to wireless charging.

2. Description of the Related Art

Portable devices has proliferated over the past ten years. For the purpose of cost and convenience these devices rely on secondary power cells which can be recharged for example laptop computers, mobile telephones, electrical toothbrushes, shavers and personal digital assistant. Many of these devices are charged via electrical contacts and power supplies that take power from the mains and convert into a level suitable for each individual device.

Conventional techniques for power conversion and electrical connection vary considerable from manufacturer to manufacturer. Therefore, for consumers who own several of these devices are required to own or carry around several different types of adaptors which can be cumbersome when traveling or trying to find enough sockets to plug them into. Moreover, these devices have open electrical contacts that can be damaged in water or exposed to other chemicals and therefore inappropriate to be used by hard wearing users. In recent years, some attempts have been made to overcome the foreseeable problems.

Inductive transference of energy or power has been used for many years in the form of transformers in switched mode power supplies. They include a primary circuit that generates electromagnetic flux field and fixed secondary circuits those receive inductively coupled power.

Wireless power transfer has become a very attractive solution with the proliferation of portable devices over the past ten years. With these devices for instant mobile phones, toothbrushes, PDA or laptop computers reliant on rechargeable secondary powered cells, it may not always be convenient or safe to have open electrical contacts. The wireless connection provides a number of advantages over conventional hardwired connections. A wireless connection can reduce the chance of shock and can provide a relatively high level of electrical isolation between the power supply circuit and the secondary circuit. Inductive couplings can also make it easier for a consumer to replace limited-life components. Secondary devices can be completely sealed to ensure safety when used in damp or wet surroundings for example bathroom, kitchen or even swimming pool. This wireless solution is not only limited to portable devices. Many devices like game consoles, DECT phones or even a lamp can benefit from cutting the cords. As there many wireless communication platforms that already exist or upcoming like Bluetooth, NFC, WIFI, UWB, GSM etc., the only physical connection left is the power supply.

Wireless inductive charging of portable devices is divided into two categories. The first category is indirect charging, where the wireless electronics supplies power to secondary of the charging circuitry of a portable device which in turn will charge its battery accordingly. The second category is direct charging, where the secondary of the wireless inductive charging electronics are connected (contacted) to the battery directly supplying the charging current. Direct charging is typically more efficient as it has less circuitry for power loss to occur. However, direct charging is physically difficult to implement using wireless technology on existing portable devices. Many portable or handheld devices are built to a compact specification. Portable devices typically do not have room for any additional circuitry.

Prior techniques of non-contact battery charging include a technique whereby an inductive coil on the primary side aligns with a horizontal inductive coil on a secondary device when the device is placed into a cavity on the primary side that ensures precision in the alignment, which is crucial to achieving effective power transfer. A device that uses this technique includes the Braun Oral B Plak Control toothbrush. However, this system requires the secondary devices to be axially aligned with the primary unit. Existing wireless chargers are typically also uniquely designed by each individual manufacturer and typically cannot be used interchangeably.

Examples of wireless power transfer include U.S. Pat. No. 3,938,018 to Dahl; U.S. Pat. No. 5,959,433 to Rohde; U.S. Pat. No. 4,873,677 to Sakamoto, et al.; U.S. Pat. No. 5,952,814 to Van Lerberghe; U.S. Pat. No. 6,208,115 to Binder; WO 00/61400; WO 95/11545; GB2399225; GB2399226; GB2399227; GB2399228; GB2399229; GB2399230; U.S. Pat. No. 5,519,262 to Wood; U.S. Pat. No. 5,703,461 to Minoshima, et al.; U.S. Pat. No. 6,906,495 to Cheng, et al.; U.S. Pat. No. 7,123,450 to Baarman, et al.; U.S. Pat. No. 4,675,615 to Bramanti; U.S. Pat. No. 5,952,814 to Van Lerberghe; U.S. Pat. No. 7,211,986 B1 to Flowerdew et al.; and U.S. Pat. No. 7,215,096 B2 to Miura et al.

Embodiments of the invention can resolve the matter of cost, size and efficiency. Embodiments can be modular giving the possibility of for user to customize to their requirements with ease. It is flexible, where it can be mould to any shapes and sizes. It is also intelligent, it can detect when and where power is used, keeping auxiliary power losses to the minimum.

A first embodiment is used as a battery charger to recharge a system of biometrics security card for used in airports. The primary is assembly can be mould onto the dashboard of vehicles, staff desks and ticketing or reservation counters using anti slip material as the surface. The secondary is mounted to the biometrics security card which has to be intrinsically safe. Multiple cards can be charged at the same time. The cards can be charged regardless of their orientation due to the rotating magnetic field produced by a thin 2-dimensional surface using a single layer multi-filar stacking technique.

A second embodiment is used as a single or multiple mobile phones charger. With a minute secondary charging circuit placed within the mobile phone, the phone can be charged when placed in the vicinity of the magnetic field regardless of orientation. The charging surface can be customized to the size used. In the event when the charging surface is larger than the required area of the mobile phone, the inductive power transfer will be localized to the device itself. This aspect reduces unnecessary power generation and its resulting losses.

One aspect is in a flexibility which is achieved using micro-tiles high permeability ferrites to form the magnetic core used as the charging surface. This charging surface is powered as the primary of the of the magnetic flux field with power electronics circuitry.

A second aspect is in this power circuitry, where anti-saturation reset inductive toroidal cores are used should the primary experience a phenomenon called the staircase saturation, which is normally the main reason for component failures. This technique prevents heating of the ferrite cores and as a result smaller and lower rated components can be used.

A third aspect is in the winding technique where a single layer multi-filiar technique is used to achieve a rotating magnetic flux field with the assistance of a unique power circuitry design. This rotating field is what enables the power transference to occur successfully regardless of orientation of the secondary assembly.